Bright and durable scintillation from colloidal quantum shells

Efficient, fast, and robust scintillators for ionizing radiation detection are crucial in various fields, including medical diagnostics, defense, and particle physics. However, traditional scintillator technologies face challenges in simultaneously achieving optimal performance and high-speed operation. Herein we introduce colloidal quantum shell heterostructures as X-ray and electron scintillators, combining efficiency, speed, and durability. Quantum shells exhibit light yields up to 70,000 photons MeV−1 at room temperature, enabled by their high multiexciton radiative efficiency thanks to long Auger-Meitner lifetimes (>10 ns). Radioluminescence is fast, with lifetimes of 2.5 ns and sub-100 ps rise times. Additionally, quantum shells do not exhibit afterglow and maintain stable scintillation even under high X-ray doses (>109 Gy). Furthermore, we showcase quantum shells for X-ray imaging achieving a spatial resolution as high as 28 line pairs per millimeter. Overall, efficient, fast, and durable scintillation make quantum shells appealing in applications ranging from ultrafast radiation detection to high-resolution imaging.

Editorial Note: This manuscript has been previously reviewed at another journal that is not operating a transparent peer review scheme.This document only contains reviewer comments and rebuttal letters for versions considered at Nature Communications.

REVIEWER COMMENTS
Reviewer #1 (Remarks to the Author): I find that the manuscript has been properly revised to account for my and other reviewers' comments.I recommend it for publication Reviewer #2 (Remarks to the Author): I would like to thank the authors for the work done and for the clarifications received.The results obtained are excellent and the work is certainly very interesting.
However, I still have some doubts related to the emphasis given to light yield and the comparison made with standard scintillators.The evaluation of light yield in this type of scintillator is certainly very delicate and complex.The authors have done a remarkable work using two different methods for estimating the light yield.However, the uncertainties on the evaluation of the light yield are very large.For example, as reported by the authors themselves, there is a difference of 15% between the evaluation of light yield with RL comparative measurements and that with the pulse height spectrum.Moreover, for what concern the RL measurement alone, there is an uncertainty of >10% on the thickness of the QS film (i.e.sample core: 4.5 nm, thickness 3429+/-444) which, through normalization, propagates on the estimate of the light yield.Moreover, also the uncertainty on the QS film density must to be taken into consideration.This is just an example to underline how difficult is the estimate of the light yield for these samples and, consequently, it is very tricky and risky to make a direct comparison with other scintillators as is done several times in the article and reported for example in Fig. 2b and Table S3.If the authors believe it is essential to make this type of comparison, I think it's better to report also the uncertainty and not only the light yield mean values or at least insert some comments on the accuracy of the measurements.Linked to this is the discussion on the energy resolution of 75% obtained in the measurement with the 55Fe source reported on page.8.For a scintillator with such a high light yield I would expect a significantly better energy resolution.Maybe an explanation for the low energy resolution obtained could be related to the fact that having a very thin film (only 5 µm) the electrons produced by the photoelectric effect can release an ever-changing fraction of their energy in the scintillator thus producing a broadening of the energy resolution.This is another example of how delicate it is to make a comparison between the energy resolution (and the light yield) of a standard 'bulk' scintillator and such a thin film.
Finally, there are some aspects that need to be double-checked within the text: -Several references are wrong such as on page.6 "sample thicknesses in Table S1" -> Table S2 or "see SI Section 1 and Figure S6" -> S8 -Some citations are reported several times in References -In Methods -Comparative light yield calculation, if alpha is the attenuation length I think that in the formula for the comparative quantum yields the exponent should be t/alpha 1 Our responses are provided below together with all modifications made in the revised manuscript.Reviewer comments are marked with yellow highlights, while changes implemented in the revised manuscript are indicated with green.Text without highlights represents our responses.
Reviewer #1 (Remarks to the Author): I find that the manuscript has been properly revised to account for my and other reviewers' comments.I recommend it for publicafion The evaluafion of light yield in this type of scinfillator is certainly very delicate and complex.The authors have done a remarkable work using two different methods for esfimafing the light yield.However, the uncertainfies on the evaluafion of the light yield are very large.For example, as reported by the authors themselves, there is a difference of 15% between the evaluafion of light yield with RL comparafive measurements and that with the pulse height spectrum.Moreover, for what concern the RL measurement alone, there is an uncertainty of >10% on the thickness of the QS film (i.e.sample core: 4.5 nm, thickness 3429+/-444) which, through normalizafion, propagates on the esfimate of the light yield.Moreover, also the uncertainty on the QS film density must to be taken into considerafion.This is just an example to underline how difficult is the esfimate of the light yield for these samples and, consequently, it is very tricky and risky to make a direct comparison with other scinfillators as is done several fimes in the arficle and reported for example in Fig. 2b and Table S3.If the authors believe it is essenfial to make this type of comparison, I think it's befter to report also the uncertainty and not only the light yield mean values or at least insert some comments on the accuracy of the measurements.
We express our grafitude to the Reviewer for recognizing our effort in esfimafing the light yield of quantum shell thin film scinfillators.We agree that accurately gauging the light yield of an ultrathin film scinfillator presents a challenge, so it is important to determine experimental uncertainfies.Following the Reviewer's suggesfions, we now report uncertainty in light yield measurements and incorporate these in the main text and SI.Furthermore, in accordance with the recommendafion, we have reduced the emphasis in comparing the LYs of QSs with those of bulk scinfillators throughout the revised text.
In the abstract: "Quantum shells exhibit superior room-temperature X-ray scinfillafion, with light yields up to 70,000 photons per MeV, surpassing the best commercial inorganic scinfillators." On page 3: "When exposed to hard X-rays of 11.5 keV, the light yield of the QSs is found to be as high as 70,000 ± 13,300 (mean ± standard deviafion) ph/MeV, befter than most commercial ceramic scinfillators." On page 6: "Therefore, the LY of these QS samples is esfimated to be as high as 70,000 ± 13,300 ph/MeV." "To independently confirm these large LYs, we use an independent method, i.e., pulse height spectrum.Using a 55 Fe radiafion source, we measure the LY of the same QS samples to be 80,000 ± 8,600 ph/MeV (see SI Secfion 1 and Figure S6).The mean values of LYs determined with two independent methods agree within 15%." "Our LY characterizafion method also showed much smaller LY (6,700 ph/MeV) when measuring a core/gradient-shell quantum dot structure. 31" "Uncertainty (~20%) in LY esfimates are higher than bulk scinfillators because of uncertainfies in thickness and density of the thin film QS samples.Despite that, mean values of the LY in QSs compare well among commercial and non-commercial inorganic, organic, perovskite and nanoparficle based bulk scinfillators at room temperature (see Figure 2b, Table S3).Figure 2b compares the LY of the QSs (marked with stars) to various commercial and non-commercial inorganic, organic, perovskite and nanoparficlebased scinfillators reported at room temperature (see Table S2 for the source data).The LY of QSs is on par with the best-reported LY levels of bulk scinfillators at room temperature."On page 7: "QSs achieve  of 34,000 ± 6,500 ph/MeV/ns" On page 16, Methods secfion: "The uncertainty in the light yield has been calculated by error propagafion method.Error in thickness is ~13% for the highest efficiency sample (4.5 nm core).Error in parficle density is ~10%.The propagated error is ~19%.Propagated errors are 16% and 17% for 6.0 and 8.2 nm cores, respecfively." We also updated Figure 2b with error bars represenfing the standard deviafion in each QS sample.
Linked to this is the discussion on the energy resolufion of 75% obtained in the measurement with the 55Fe source reported on page.8.For a scinfillator with such a high light yield I would expect a significantly befter energy resolufion.Maybe an explanafion for the low energy resolufion obtained could be related to the fact that having a very thin film (only 5 µm) the electrons produced by the photoelectric effect can release an ever-changing fracfion of their energy in the scinfillator thus